We find that \(\Delta _\phi \)  is within 1 of zero in 20% of cases, \(\Delta _\phi > 1\)  in 62% of pulsars and \(\Delta _\phi < -1\)  for 18% of the population (see Table REF ). This strong bias towards positive values indicates the [1]} effect at work. Figure REF  shows \(\Delta _\phi / W\)  versus \(\dot{E}\) . Here we see that virtually all pulsars with \(\dot{E} > 10^{34}\)  erg s\(^{-1}\)  have \(\Delta _\phi /W > 0\) (53 out of 61 cases). This is likely due to a combination of short \(P\)  and high heights (cf Equation REF ). For pulsars with \(\dot{E} < 10^{34}\)  erg s\(^{-1}\)  there remains a strong bias towards positive values of \(\Delta _\phi /W\)  (262 out of 350 cases). Some of the pulsars with negative \(\Delta _\phi \)  are so-called `partial cones' which are dealt with in more detail in subsection 5.6.
